A resin-made fuel tank in an automobile or other vehicles usually includes a fuel pump inside the tank. Fuel is made to pass through a fuel supply passage connected to the fuel pump, and is supplied to an engine from the fuel tank. The fuel tank has an opening section so as to install the fuel pump. After the fuel pump has been installed in the fuel tank, the opening section is sealed with, for example, a lid member through which the fuel supply passage penetrates. There are, however, some gaps between the above opening section and the lid member. Thus, there are provided various seal structures so as to prevent fuel leakage through such gaps.
For example, Patent Documents 1 and 2 disclose that a seal member or another member is disposed inside an opening section. In addition, Patent Document 3 discloses use of an outer wall thread for the opening section.